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Genetic analysis of snowshoe hare population structure Burton, Cole

Abstract

Snowshoe hares are distributed throughout the boreal forests of North America and play a key role in the functioning of these ecosystems. Very little is known about the social and genetic structure of snowshoe hare populations. In this thesis, I used seven microsatellite DNA markers to investigate three levels of hare population structure: mating structure, social structure and geographic structure. I sampled 382 hares at 12 sites in southwestern Yukon (separated by 3-140 km) from April to August 1999, during a peak phase of the 10-year hare cycle. I also obtained samples from interior Alaska (n = 27) and western Montana (n = 19) for comparison. Genetic diversity was high, with 5 to 37 alleles per locus (mean = 13.4) and an overall expected heterozygosity of 0.67. At the level of mating structure, the genotypes of 65 newborn hares from 17 litters indicated that multiple paternity occurred at a low to moderate frequency (-25-30%), and that reproductive success was fairly widespread among male hares. In terms of social structure, the comparison of genetic relatedness with spacing behaviour among 68 hares on two 7.3 ha grids revealed that average group relatedness was low, and that related hares were not more likely to associate with each other than non-related hares. At a larger geographic scale I found significant genetic heterogeneity. The degree of genetic differentiation was low among Yukon sites (FST = 0.015) and between Yukon and Alaska (FST = 0.012); however the Montana site was highly differentiated (FST = 0.20). Geographic distance and landscape barriers explained some of the genetic differentiation between sites, but in general were poor predictors of geographic genetic structure. The indication of considerable long-distance gene flow implies that previous field observations may have underestimated dispersal, but confirms that hare dispersal is widespread, successful and equal between the sexes. The results of all three levels of investigation suggest that snowshoe hares have little population structure in southwestern Yukon during a cyclic peak phase. Hares do not form stable breeding groups, do not live in kin clusters, and do not experience significant social or physical barriers to gene flow across large areas. Future studies focusing on different phases of the hare cycle, and different regions, will be critical for understanding the mechanisms that shape the genetic structure of snowshoe hare populations.

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